I'll see if I can dig up some of those books. As for the mention in the OP, whaddeva. :)

Here are some very cool photos of some underground sites in Japan, etc.

And it looks like these might be some of the books you mentioned. Niiiiiiice.

You found them! The "Japan Underground" series is really too cool for words.

Don't forget about the famous Paris sewer system, the underground lake at the Paris Opera House (Opera Garnier), and the underground city in Seattle

wowzer! incredible pics.

there are tons of places with vast undergrounds just begging to be explored by those with the interest (and more than a little guts). I remember tales from my dad of huge underground storage areas in Hawaii used for fuel storage, bunkers...etc

makes me wonder what else is going on 'down there'

Oh, I haven't. And hopefully someday I'll see them with my own eyes.

I don't know if this qualifies, but I grew up in New York apartment buildings where the basements all displayed prominent yellow "fallout shelter" signs. I could never quite figure out where the shelters actually were. Maybe it was the entire basement. If that was so, then the black men who worked in the building and lived in basement apartments were very lucky.

Underground Chinatown.

I read about this sort of thing in a young adult book (Kiki Strike) actually. Nifty, nifty!

Yes, we do have an underground city in Seattle. People LOVE this tour!!! Personally, I'm way too claustrophobic to attempt it but my hubby and son have done it.

I'm so amazed that so long ago they could actually build a whole city on top of another. Sure, it was done a little at a time, but I picture what it took to build the city under WDW and they had heavy machinery (and a lot less time of course). This is an interesting subject!